An apparatus of the previously mentioned kind serves to create a so-called cardiokymogram (CKG) which especially in combination with an electrocardiogram (EKG) can provide information as to whether the heart muscle upon stimulation by impulses visible in the EKG contracts in an orderly way. The heart wall movement continues to the tissue and can be detected on the outer surface of the breast as a very small movement of the skin. This movement can for example be detected if the outer surface of the skin and an electrode form a condenser contained in the frequency determining portion of an oscillator. One such movement of the skin causes a change in the capacity of such condenser and thereby a change in the oscillation frequency of the oscillator. The thereby evoked frequency modulation permits the production of a signal representing the heart wall movement.
The movement to be captured has a very small amplitude and is therefore not only influenced by the properties of the tissue and of the skin, but is also superimposed on body movements produced by breathing or otherwise. With a previously known apparatus of the aforementioned kind, it was possible to obtain usable signals only under laboratory conditions and through absolute quieting of the patient to be examined. With this, however, it was not previously possible to create a CKG with simultaneous stressing of the patient's body. Basically heart flaws can usually first be discovered with body stressing of the patient. For this, portable measuring devices have already been made which make possible the obtainment of a 24 hour EKG. The parallel taking of a CKG over the same amount of time was not possible with the previously known measuring apparatus.